Release of cell-free ice nuclei by Erwinia herbicola

Abstract

Several ice-nucleating bacterial strains, including Erwinia herbicola, Pseudomonas fluorescens, and Pseudomonas syringae isolates, were examined for their ability to shed ice nuclei into the growth medium. Only E. herbicola isolates shed cell-free ice nuclei active at -2 to -10°C. These cell-free nuclei exhibited a freezing spectrum similar to that of ice nuclei found on whole cells, both above and below -5°C. Partially purified cell-free nuclei were examined by density gradient centrifugation, chemical and enzymatic probes, and electron microscopy. Ice-nucleating activity in these cell-free preparations was associated with outer membrane vesicles shed by cells and was sensitive to protein-modifying reagents.

Ice nucleation by fertile soil dusts: relative importance of mineral and biogenic components

“…Indeed, previous estimates of the numbers of live ice-nucleating bacteria in soils have been unable to account for observed ice active site densities (Conen et al, 2011). Non-viable cells, cell membrane fragments and membrane vesicles have all been shown in the laboratory to exhibit IN activity (Maki and Willoughby, 1978;Phelps et al, 1986;Hartmann et al, 2013;Augustin et al, 2013), and dead bacteria have been postulated to contribute significantly to the ice-nucleating ability associated with plant tissues (Ashworth and Kieft, 1995;Lindow, 1983a, b). While the lifetime of IN active proteins derived from bacteria and fungi in soils is unknown, there is evidence to suggest that certain proteins in soils can have extremely long residence times, on the order of centuries (Amelung et al, 2006).…”

Laboratory Study of Effects of Atmospheric Pollutants on Ice Nucleation Activity of Bacteria

“…Moreover, some studies have shown that the variability of nucleating frequencies is a function of seasonal and diurnal changes for some bacterial populations (Hirano and Upper, 1989). The dead and even the cell-free nuclei of some kinds of bacteria exhibited freezing properties (Anderson and Ashworth, 1986;Phelps et al, 1986). Cochet et al (1994) also have shown that pH negatively influences the bacterial nucleation activity.…”

Enhanced production of extracellular ice nucleators from Erwinia herbicola.

“…Although shedding of ECINs was quite variable in quantity, usually 10 to 30% of the INA at Ϫ4°C was associated with ECINs when E. herbicola cells were grown on YE medium at 20°C (data not shown). Phelps et al (1986) reported that an average of 10% of the total ice nuclei from E. herbicola M1 were cell-free and active at Ϫ3°C when grown on a minimal glycerol medium at 15°C.…”